The present invention relates to a method of detecting the position of an inner surface of a piece for machining or measurement on a machine tool. More specifically, the present invention may be used to advantage, though not exclusively, for detecting the position of inner surfaces of dead and/or particularly long hollow bodies whose inner surfaces are practically invisible from the outside and difficult to measure or detect using known equipment.
When machining hollow pieces of the above type, the exact position of the inner surface must be known to set the tool to a zero position in which the cutting edge of the tool skims the inner surface, and which is used as a reference for various internal machining operations, such as boring, face machining dead seats or shoulders, or for making measurements.
At present, zero positioning of the tool is performed manually by the operator easing the tool into contact with the inner surface for machining. Depending as it does on the skill and sensitivity of the operator, such a method obviously involves macroscopic errors which are unacceptable in finish machining operations and, in general, in any operation involving the removal of minute amounts of material, and conformance with strict machining tolerances, normally in the region of a hundredth of a millimeter.
It is an object of the present invention to provide a method of detecting the position of an inner surface of a workpiece on a machine tool, designed to provide a straightforward, low-cost solution to the above problem.
According to the present invention, there is provided a method of detecting the position of the inner surface of a hollow metal workpiece on a machine tool; the method comprising the steps of inserting an operating member of the machine inside said hollow workpiece, and moving the operating member gradually towards said inner surface; and being characterized by connecting to a first terminal of an electric power source a metal portion of said operating member, which is to be brought into contact with said inner surface; connecting said inner surface to a second terminal of said power source; determining the instant of emission of a signal generated by emitting means interposed between one of said terminals and one of said operating member and said inner surface, and corresponding to a condition in which initial contact is established between the operating member and said inner surface; and determining the position of said operating member at said instant of emission.
The present invention also relates to a chip-forming machine tool.
According to the present invention, there is provided a chip-forming machine tool comprising a bed; retaining means for retaining a hollow metal workpiece defined by an inner surface; an operating member having at least one metal portion for at least contacting said inner surface; and actuating means for moving said operating member to and from said inner surface; characterized by also comprising an electric power source having a first and a second terminal; first electric connecting means interposed between said first terminal and the metal portion of said operating member; second electric connecting means interposed between said second terminal and said inner surface; emitting means interposed between one of said terminals and one of said operating member and said inner surface, and for emitting a signal the instant initial contact is established between the operating member and said inner surface; and display means for indicating the position of said operating member at said instant of contact.